Android Failed to resolve: com.a

首先：检查项目下的build.gradle是不是27+

compileSdkVersion 27
buildToolsVersion "27.0.3"

项目根目录build.gradle

allprojects {
    repositories {
        jcenter()
        mavenCentral()
        maven{url "https://jitpack.io"}
        maven{url "https://maven.google.com"}
    }
}